The use of chain or belt mounted pusher elements is well known in the art of paper handling. Such pushers are used to push a sheet, group of sheets, or folded insert from an upstream position, down a guide path, and into an envelope, which is typically held stationary for an instant to permit insertion of the sheet, group of sheets, or folded insert.
One conventional device, disclosed in U.S. Pat. No. 6,283,276, assigned on its face to Bell & Howell Mail and Messaging Technologies Co. of Durham, N.C., and incorporated herein by reference in its entirety, utilizes two side-by-side overhead pusher finger guides or pushers used in tandem so that the insert (whether a flat or folded sheet or group of sheets) received at the upstream position will not skew prior to or at the time of insertion of the insert into the waiting envelope. Another conventional chain-driven device, disclosed in U.S. Pat. No. 5,806,659, also assigned on its face to Bell & Howell Mail and Messaging Technologies Co. of Durham, N.C., and incorporated herein by reference in its entirety, utilizes a lightweight chain apparatus bearing a plurality of spaced-apart pusher members attached to the chain and a guide element intended to improve dimensional stability of the pusher members.
A conventional overhead conveyor 10 in accord with U.S. Pat. No. 6,283,276 is depicted in FIG. 1. First and second circular drive members, such as sprockets 15, 20, are mounted on rotatable drive shafts 16, 17, respectively. Sprockets 15, 20 are positioned such that the X axis is tangent to the lowermost point of each of sprockets 15, 20 and, therefore, the lowermost point of each of sprockets 15, 20, lie along the same point of the Z (vertical) axis. Drive shaft 16 is connected to drive motor 25, and endless conveyor chain 30 is wrapped around the teeth of sprockets 15, 20 and comprises upper conveyor chain run 30a and lower conveyor chain run 30b. Slack in upper conveyor chain run 30a is prevented by use of one or more idler sprockets 32, 34 and, with suitable positioning thereof, lower conveyor chain run 30b will be parallel to the X axis, which itself is parallel to the downstream paper feed direction F. Alternatively, overhead conveyor 10 may be an endless belt-based conveyor, in which case, the circular drive members would comprise pulleys.
A plurality of pusher elements 40 are attached to conveyor chains 30 at a fixed spaced-apart distance. Each pusher element has a lower portion 40a for supporting the bottom of a sheet(s) and an indented portion 40b for receiving the rear portion of sheet(s) and pushing the same in paper feed direction F. To control the degrees of freedom of movement allowed of pusher 40, a guide 100 is provided for assuring pusher element 40 moves only in the X direction with no deflection in the Y or -Z directions. Guide 100 comprises a guiding element 50 of a selected cross-sectional shape (e.g., a circular cross-section). Sidewalls 42 of the pushers 40 are configured to straddle the respective guiding element 50.
Motor 25 drives conveyor chain 30 and guide elements 40 (rigidly fixed to endless conveyor chain 30) in the counter-clockwise direction through drive shaft 16 and sprockets 15, 20.
At the beginning of a feed cycle for an incoming sheet or plurality of sheets or folded sheet of plurality of sheets in direction F, pusher element 40 on an upper run 30a of endless conveyor chain 30 starts to pass downwardly around sprocket 20 and approaches guide element 50 of guide 100 at the bottom half of sprocket 20. The sidewalls 42 of pusher element 40 start to receive therebetween (e.g., straddle) guide element 50, and thereafter a horizontal cross wall 39 of pusher element 40 comes into contact with the top of guide element 50. Once pusher element 40 passes around sprocket 20 and into lower run 30b of endless conveyor chain 30, indented portion 40b of pusher element 40 contacts the sheet and pushes it in direction X (paper feed direction F) until it reaches a designated release point (not shown), at which time the sheet S is released and pusher element 40 moves upwardly around sprocket 15 and out of engagement with guide element 150 to permit repetition of the cycle.
Despite the improvements realized by the above configuration, there still remains room for improvement in the art, particularly given the movement of sheets, packets, or inserts under increasingly large accelerations and speeds, both absolute and differential or relative, despite the above-noted improvements to the dimensional stability of the pushers. Thus, there exists a need for a pusher finger guide that reduces opportunity for sheet skew.